1. Field of the Invention
The present invention relates to producing a selective hydrodenitrogenation catalyst which is effective in the removal of nitrogen from an organic material. More specifically, the present invention relates to the preparation and use of catalysts which comprise transition metal compounds, cobalt or nickel and molybdenum which improve hydrodenitrogenation under conditions of heat and pressure.
2. Description of the Prior Art
Hydrodenitrogenation (HDN) is the catalytic process by which nitrogen is removed as ammonia when feedstocks, such as petroleum, are refined to produce fuel or petrochemical feedstocks. HDN is also an important step in the conversion of coal, coal liquids, oil shale, tar sands, residues and the like to synthetic fuels. If nitrogen is not removed during the refining of the hydrocarbon feedstocks, during subsequent refining, products form having undesirable characteristics. For example, the basic nitrogen-containing species can effectively poison the acid hydrocracking and reforming catalysts used in the refining process. Consequently, HDN is vital and necessary to produce high-quality, low-cost fuels and feedstocks.
At an industrial level, HDN catalysis is usually performed using heterogeneous catalysts consisting of either cobalt molybdenum oxides (CoMo), nickel and tungsten oxides (NiW) or nickel and molybdenum oxides (NiMo) supported on alumina (Al.sub.2 O.sub.3 or Al.sub.2 O.sub.3 --SiO.sub.2). HDN is usually performed at about 350.degree.-500.degree. C. and up to several thousand psi of hydrogen pressure.
It is generally difficult, to effectively evaluate CoMo- or NiMo-catalyzed HDN of crude feedstocks. Solvent refined coal (SRC) as a feedstock has been used to evaluate some catalyst performance. Usually, catalysis studies are conducted on model compounds, such as pyridine, indole or preferably quinoline. These model compounds most closely resemble the basic nitrogen - containing compounds found in feedstocks. Studies performed with NiMo catalysts and quinoline have resulted in the HDN reaction network shown in Reaction Sequence l in FIG. 1. The ideal HDN catalyst should have high C-N bond activity while having low hydrogenation activity, therefore selectively producing more aromatic compounds. Thus, in comparing the effectiveness of the HDN catalysts, the proportion of propylbenzene (4 moles H.sub.2 required) to propylcyclohexane (7 moles H.sub.2 required) is a key measure of the hydrogen consumption.
Some general observations are made by R. Laine on the mechanisms of heterogeneous catalysis in the hydrodenitrogenation reaction in Catalytic Reviews of Science and Engineering, Vol. 25, No. 3, Pages 459-474 published in 1983, which is incorporated herein by reference. Laine discusses the catalytic clevage of saturated C-N bonds in the a transalkylation reaction at 125.degree. C.: R.sub.3 N+R'.sub.3 N.fwdarw.R.sub.2 NR'+R'.sub.2 NR in the presence of metal carbonyls, such as Ru.sub.3 (CO).sub.12.
Other reports of research in this area include the following:
In U.S. Pat. No. 4,504,589, Ryan discloses a method and a catalyst having improved hydrodenitrification (hydrodenitrogenation-HDN) activity. The hydrotreating catalysts have catalytically active amounts of Group VIII and/or Group VIB metals incorporated into a support which comprises adding from about 0.5 to 15 percent by weight of molybdenum and/or tungsten carbonyls to the catalyst by sublimation and drying and calcining the metal carbonyl impregnated catalyst. The specific metal carbonyls examined were molydbenum, chromium and tungsten which were sublimed onto a commercial nickel/molybdenum/Al.sub.2 O.sub.3 hydrotreating catalyst. After calcining the metals added were assumed to have the form MoO.sub.3, CrO.sub.3 and WO.sub.3.
In European Patent Organization No. 50911, A. W. Tait et al. disclose a catalyst and process for the hydrodenitrogenation and hydrocracking of high-nitrogen feedstocks. A catalyst is disclosed which comprises a hydrogenation component itself comprising chromium, molybdenum, and at least one metal of Group VIII, a crystalline molecular sieve zeolite, and a porous refractory inorganic oxide. Zeolites having pore diameters of at least 5 Angstroms and containing exchangeable cations are suitable. These include faujasite-type crystalline alumino-silicates, ZSM5-type crystalline aluminosilicates and others.
In European Patent Organization Pat. No. 133031, R. R. Chianelli et al. disclose bulk and supported, self-promoted molybdenum and tungsten sulfide catalysts formed from bis (tetrathiometallate) precursors and their preparation and use for hydrotreating. Metal promotors such as nickel, cobalt or iron are disclosed.
S. H. Yang et al. in the Journal of Catalysis, Vol 81, Pages 168-178 (1983) disclose a method of presulfiding a commercial NiMo/Al.sub.2 O.sub.3 catalyst which has a significant effect on its activity for the HDN of quinoline. Further during the reaction the addition of H.sub.2 S increases the HDN rate and its removal decreases the rate in a reversible manner.
Y-YP. Tsao in U.S. Pat. No. 4,513,098 discloses the preparation of highly dispersed multimetallic catalysts and their method of preparation from organometallic precursors. These catalysts are prepared by contacting the surface hydroxyl-containing inorganic oxide support with a metal pi-complex organometallic precursor such as molybdenum tetroallyl. The resulting product may be reduced or sulfided to form a catalyst of high activity.
T. G. Harvey et al. in J. Chem. Soc. Chem. Commun., Pages 188-189 (1985) discloses that sulphided ruthenium supported on a Y-Zeolite is a very active catalyst for hydrodenitrogenation. This catalyst when physically combined with sulphided nickel molybdate on alumina produces a catalyst in which the activity is enhanced. The ruthenium-containing Y-zeolite is prepared by ion exchange with Ru(NH.sub.3).sup.3+.sub.6. The selectivity of the catalyst is not examined.
Additional references of interest include:
T. J. Lynch et al., J. Molec. Cat., Vol. 17, Pages 109-112 (1982).
T. J. Lynch et al., "Iron Carbonyl Catalyzed Reductions of Model Coal Constituents Under Water Gas Shift Conditions" Preprints, American Chemical Society, Division of Fuel Chemistry, Vol. 28, No. 1, Pages 172-179 (1983).
R. H. Fish, "Homogenous Catalytic Hydrogenation .3 Selective Reductions of Polynuclear Aromatic and Heteroaromatic Nitrogen Compounds Catalyzed by Transition Metal Carbonyl Hydrides", Ann of New York Acad. Sci., (ed. D. W. Slocum, et al.) Vol 415, Pages 292-301 (1983).
L. J. Boucher, et al., "New Catalysts for Coal Liquid Upgrading--Final Technical Report", Dept. of Energy Report No. DOE/PC/40812--T11 (DE84 015921), Aug. 15, 1984.
None of these references disclose the present invention.
With present technology most of the quinoline undergoes HDN by the darkened pathway of FIG. 1 which ultimately produces primarily propylcyclohexane. This pathway uses almost twice as much hydrogen as the other pathway that produces the more desirable (and higher octane) propylbenzene.
If NiMo or CoMo catalytic activity for C--N bond cleavage is enhanced relative the catalyst activity for hydrogenating the aromatic ring, a considerable savings in hydrogen costs and a more useful hydrocarbon product would be obtained. The present invention provides process and catalysts to achieve higher C--N bond cleavage with a reduction in hydrogenation. The present invention is also expected to be useful in hydrodeoxygenation (HDO) and hydrodesulfurization (HDS). The result is a significantly cheaper refined fossil fuel.